Is Ground-Penetrating Radar Accurate?

Ground-penetrating radar, or GPR, is a surveying technique that uses electromagnetic waves to detect and map the subsurface. It has been used for decades – but how accurate are these scans?

The Accuracy of Ground Penetrating Radar (GPR) Technology

Ground-Penetrating Radar is a highly accurate tool! Ground-penetrating radar can be impacted by external factors, but proper use of equipment and interpretation of readings should result in a high accuracy rate. This blog post will discuss the ways that GPR is used, how it works, what you can locate with it, and how Sentry Mapping uses GPR in our services.

What Is Ground Penetrating Radar and How Does it Work?

Ground-penetrating radar (GPR) is a geophysical method of testing used to determine the location of objects below the earth’s surface by measuring their reflection and transmission of electromagnetic waves. It has become increasingly common in archaeological, engineering, geologic, and environmental work over the past 30 years.

picture of multiple tomb stones in cemetery packed closely together

Locating Underground Anomalies with GPR Equipment

GPR uses high-frequency antennas to emit radio waves with frequencies between 1MHz and 3GHz that are transmitted vertically into the ground from antennas on top of poles or towers. 

The resolution of Ground-Penetrating Radar images can be increased or decreased through the use of different antennae frequencies. Generally speaking, higher frequencies produce more detailed images but require longer scanning times.

The energy in these waves can penetrate through many different types of soils but is reflected when it encounters an object underground such as a rock, wood, bone, or metal pipe. 

A recording device measures how long it takes for each signal to be received after being sent out. This time delay provides information about changes in soil density which allows us to accurately estimate the depth of utility lines, grave sites, and other subsurface anomalies.

GPR can be used to:

  • Locate unmarked gravesites
  • Utility locating
  • Find underground voids
  • Scan concrete
  • Help with archeological digs
  • Locate underground tanks, pipes, and drums
  • map the depth of a shallow water table
  • identify soil horizons and the bedrock subsurface
  • demarcate trench boundaries
  • And much more!

Find Unmarked Graves & Underground Utilities with GPR

GPR is an accurate method for finding unmarked graves or abandoned burial sites and is often used in conjunction with GPS/GIS systems to find gravesites that are not easily located, were left unmarked, or are no longer present in cemetery rosters. Cemetery Managers often hire GPR service providers to create cemetery burial plot maps and ensure their data is accurate and the land can be used to its full potential.

Ground-Penetrating Radar is also commonly utilized to detect the presence of underground utility lines such as pipelines, water tanks, phone and internet lines, gas lines, and much more. GPR is very effective for quickly locating underground utilities, and is often used to detect the presence of buried infrastructure before excavating.

Ground Penetrating Radar is useful when performing construction excavation work. With our grounding radar GPR signal to scan the construction site before digging, we can locate any existing utility lines that could be damaged during excavation. This can be incredibly helpful as it prevents serious injury or even death due to a digging error.

Ground Penetrating Radar Equipment and Soil Content

GPR is an effective method for detecting subsurface anomalies because it is a reflection-based technique. It is important to note that GPR is not suitable for all soils, and features such as water content or soil moisture can affect the quality of data collected using this equipment.

Ground-Penetrating Radar’s penetration depth can reach up to 15 meters in sandy soil or massive dry materials such as granite and limestone. For soil with more conductive materials, electromagnetic energy dissipates faster. This causes a signal loss at depth because the electromagnetic energy is more quickly dissipated into heat. In highly conductive substrates, such as those with large amounts of clay soils, water, and/or salt, penetration depth can be only a few centimeters.

What Do the Experts Have to Say About the Accuracy of GPR?

A recent study by researchers at the University of Arkansas found that ground penetrating radar is not as accurate as previously believed. The research team discovered errors in GPR data caused by electrical interference from power lines, humidity levels, moving targets (like people), and other sources of noise. 

This means that many of the readings produced by this technology have inaccuracies greater than 25%. As a result, engineers may need to spend more time analyzing their findings before putting them into practice. 

It can be difficult to tell what GPR finds on a scan as there is no standard way to interpret the data. This makes it easy for people who are inexperienced with GPR to misinterpret what they see on the screen and send out false reports or make inaccurate conclusions about an area of land. 

picture of tombstones in a cemetery in black and white

Sentry Mapping is an Accurate GPR Service Provider

Sentry Mapping is a leading provider of geophysical services in the United States, including ground-penetrating radar surveys. We utilize industry-standard equipment and methods to ensure accuracy when conducting utility locating & mapping, archeological site location, cemetery mapping, drafting, and grave locating services.